Abstract

Analysing the levels of physical activity in childhood and adolescence through an accelerometer has become a surging avenue of study this decade, in addition to analysing maximum oxygen consumption as an important predictor and marker of health. The overall objective of this doctoral thesis was to describe the levels of physical activity and different bouts of data integration during different activities at school and outside school, as well as to analyse the association between intensities of physical activity and maximum oxygen consumption in children in primary and secondary school.
A total of 668 GT3X triaxial accelerometers were placed on students aged 8 to 19 to analyse the patterns, levels of physical activity and bouts performed. The participants wore the accelerometers on their right hip for 7 days with an “epoch” of 1 s and the cut-off points described in Evenson et al. (2008). A recording time of ≥ 10 hours/day and 5 days was considered valid. The physical activity in each of the different weekly activities was calculated: the weekly total, weekend, Monday to Friday (school week), extracurricular activities, physical education, recreation and other activities that included neither recreation nor physical education (min/day, min/hour and %). Additionally, we analysed the net and cumulative bouts corresponding to the intervals of 1, 2, 4, 5, 6, 8, 10 and 12 minutes (bouts/day and min/day). Furthermore, we performed a total of 503 tests in order to find maximum oxygen consumption. The portable analyser chosen was the Metamax 3B when participants performed the progressive maximal Chester Step test on a Swedish gymnastics bench.
The most significant results showed that a) the different methodological criteria in the use of accelerometers hindered their comparison despite having some common points; b) the best predictors of maximum oxygen consumption were age, sedentary time per day and body mass index; c) the levels of physical activity and compliance with recommendations were low; recreation and physical education allowed the participants to accumulate more physical activity at moderate to vigorous intensities per hour than the other activities; d) differences were found in the levels of physical activity as well as in net and cumulative bouts during recreation, physical activity and the remaining daily activities; the results suggest different behavioural patterns in the bouts depending on whether they are analysed as net or cumulative bouts; e) the students must avoid remaining sedentary more than 15 minutes during recreation in order to have a greater chance to have the maximum oxygen consumption listed as unhealthy.